Fish Oil May Have Been Oversold

The evidence that supplements help is weak — and yours may not even live up to their labels.

In the 1970s, Danish physicians noticed that Inuits living on the west coast of Greenland were much less likely to die from heart disease than other Danes. Both populations ate about the same amount of fat, but the Inuits were getting more of their fat from fish rather than meat. This was the beginning of 40 years of research on the effect of fish oil on human health — with uncertain conclusions. The most recent large clinical trials have not found fish oil supplements effective against heart trouble.

There’s no doubt that the “omega-3” polyunsaturated acids plentiful in fish like salmon, mackerel, and sardines are an important part of a balanced diet. Unlike plant sources such as flaxseed and canola oils, fish and marine oils derived from algae contain “DHA” and “EPA,” or essential fatty acids, which we must consume because our bodies need them and we can’t make them ourselves. Among other roles, essential fatty acids help us to form the membranes around our brain cells and may reduce inflammation, which is associated with many problems.

The Food and Drug Administration has approved prescription types of fish oil to treat unusually high triglycerides, a risk factor for heart disease. However, according to a well-publicized review in the prominent journal JAMA Internal Medicine, 24 quality studies were published in widely-read scientific journals from 2005 through 2012. Most of them focused on whether fish oil could prevent cardiovascular events in people at risk. Only two of the 24 concluded that supplements with fish oil beat a placebo.

Some researchers argue that the jury is still out about whether fish oil is protective against heart disease for the general population, rather than those already at risk. Others note that heart-disease care has improved, and fish oil may not have much to contribute for those already in treatment.  

Clinical trials of fish oil for any number of purposes have been disappointing. If you are pregnant or nursing, you may hear that these supplements can stave off pre-term births, make your baby smarter, prevent allergies in infants, or protect you against post-partum depression. But recent overviews of studies on these topics came up negative or inconclusive. There’s also been a flurry of excitement that fish oil supplements could help ward off major depression or dementia or other mental decline in the elderly; here, too, the evidence is lacking or weak. Ditto for hope that the pills could help children with autism or attention deficit disorder or people with multiple sclerosis.

Is eating more fish a good idea? Researchers have looked at the connections between dietary intake of essential fatty acids and prostate and colorectal cancer among many conditions without finding a good case that you can protect yourself against disease.

On the other hand, it remains true that we need to get essential fatty acids from our diet. The American Heart Association (AHA) recommends eating fatty fish at least twice a week, as long as the fish is broiled or baked, not fried. Although the mercury in fish can be dangerous for children and pregnant women, the AHA advises that the benefits of fish outweigh the risks of mercury for people past middle age. Fatty fish is expensive — but so are supplements.

If you opt for a supplement, look for a trustworthy brand, but avoid them if you're allergic to fish. In 2013, fish oil sales turned down amid concern about the quality of supplements. Unlike prescription medications, supplements are unregulated and may not contain what you think you’re buying. Fish oil labels are wildly inaccurate, according to the testing company Labdoor.com, which can steer you to reliable products.